resources: tidy __request_region()

No functional change.  Just return NULL for kzalloc failure immediately,
rather than wrapping the whole function body in the body of an "if".

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>